![]() Watch the short film The Making of the Fittest: Natural Selection and Adaptation. ![]() MATERIALS genetic code chart (see page 7 of this handout or a biology textbook) blue, red, and green colored pencils Molecular Genetics of Color Mutations in Rock Pocket Mice LESSON STUDENT HANDOUT Natural Selection and Adaptation PROCEDURE 1. This results in translation being stopped before the amino acid sequence of the protein is completed. Nonsense mutation: This mutation causes the protein to be truncated (cut short) due to the incorporation of a “stop” signal into the DNA sequence.This type of mutation causes a change in the primary structure of the protein (the linear sequence of amino acids), which typically results in a change in the three-dimensional conformation of the protein. Missense mutation: This mutation causes an amino acid in the sequence to be changed to another amino acid.Silent mutation: This mutation does not cause a change in the amino acid sequence of the protein therefore, there is no change in the resulting protein.Potential Results a Gene Mutation Has on a Protein The deletion of nucleotides can result in frameshift mutations. Deletion mutation: The loss of one or more nucleotides from the DNA gene sequence.The insertion of nucleotides can result in frameshift mutations. Insertion mutation: The addition of one or more nucleotides to the DNA gene sequence.Mutations that affect a single nucleotide are called point mutations. Substitution mutation: The replacement of one nucleotide of DNA for another.There are several types of mutations, and several results that mutations can have on the amino acid sequences of proteins. A change in protein structure can change, negate, or have no effect on function. Gene mutations can change the structure of the resulting protein. GENE MUTATION A gene mutation is any change in the DNA sequence of a gene. The mutated version of the Mc1r gene, however, triggers melanocytes to increase the production of eumelanin, resulting in the dark coat-color phenotype. The melanocytes of wild-type (nonmutant) mice produce more pheomelanin than eumelanin. This receptor is found embedded in the membrane of melanocytes, which are cells specialized for pigment production. This gene encodes a protein called melanocortin 1 receptor (MC1R). The synthesis of these pigments is controlled by the products of several genes, including the Mc1r gene. THE MC1R GENE The coat color of rock pocket mice is primarily determined by two pigments: eumelanin, which is dark colored, and pheomelanin, which is light colored. Through their analyses, they discovered a mutation in the Mc1r gene that is involved in coat-color determination. Researchers analyzed the data from these two populations to search for the genetic mutation responsible for the dark coat color. ![]() Scientists have collected data from a population of primarily dark-colored mice living in an area of basalt in Arizona’s Pinacate lava flow, as well as from a nearby light-colored population. But populations of primarily dark-colored rock pocket mice have been found living in areas where the ground is covered in a dark rock called basalt, which was caused by geologic lava flows thousands of years ago. Because most rock pocket mice have a sandy, light-colored coat, they are able to blend in with the light color of the desert rocks and sand that they live on. Molecular Genetics of Color Mutations in Rock Pocket Mice Published July 2012 Revised October 2013 LESSON STUDENT HANDOUT Natural Selection and Adaptation MOLECULAR GENETICS OF COLOR MUTATIONS IN ROCK POCKET MICE INTRODUCTION THE ROCK POCKET MOUSE The rock pocket mouse, Chaetodipus intermedius, is a small, nocturnal animal found in the deserts of the southwestern United States.
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